1. Field of the Invention
This invention relates to various improvements to the methods and apparatus disclosed in U.S. Patent Publication Nos. 2009/0062782 and 2009/0149845, and other similar laser treatment methods and apparatus involving monitoring of the treatment site for conditions such as overheating. The improvements include:    a. Provision of a structural element made of a material that absorbs selected wavelengths of radiation emitted during the surgical procedure, and that in response heats up or emits radiation in a way that can more easily and reliably be detected by the treatment site monitoring arrangement, whether by monitoring radiation transmitted back through the laser deliver conduit or fiber, or by a sensor or detector at the treatment site;    b. Use of other coatings to enhance detection, such as inclusion of a dark coating material to increase contrast between parts of an instrument that are overheating and other parts of the instrument;    c. Positioning of a overheating detector of the type disclosed in the parent application on a bare fiber rather than in an introducer or catheter; and    d. Provision of an improved treatment site monitoring method.
The above listed improvements may be used separately or in any combination with each other or with any elements of the system disclosed in U.S. Patent Publication Nos. 2009/0062782 and 2009/0149845, or in combination with other surgical laser methods and systems, including those described in U.S. Patent Publication Nos. 2009/0062782 and 2009/0149845 as prior or related art. While the methods and apparatus of the invention may be used with a variety of surgical laser procedures, it is especially useful for urological and varicose vein treatment applications where thermal runaway has been a particular problem.
The structural element of the invention may be disposed in or integrated with an instrument, such as a coating on an endoscope, introducer, or any other instrument present at a location where overheating might occur. Alternatively, the structural element may be a discrete element such as a sheath that can be inserted into the instrument or disposed to protect any part of the instrument and/or tissues at the treatment site. If the structural element is a sheath, then the sheath may be arranged to be inserted into an endoscope with the fiber withdrawn slightly into the sheath, thereby protecting the working channel of the endoscope from mechanical damage from the relatively sharp tip of the fiber without interfering with movement of the fiber.
In addition, the apparatus of the invention may include or be used with components for monitoring radiation absorption by the radiation absorbing structural element, either by monitoring the temperature of the radiation absorbing structural element, or by monitoring radiation emitted by the structural element.
Still further, a support guide may be added to ensure that the fiber tip avoids contact with the working channel of an instrument such as an introducer or endoscope.
2. Description of Related Art
A number of copending patent applications, prior patents, and prior publications, address the problem of detecting and preventing damage due to overheating of tissues and/or instruments/devices used to deliver laser energy to tissues during laser surgery or therapeutic laser procedures. For example, U.S. Patent Publication No. 2009/0062782 (based on U.S. patent application Ser. No. 12/047,819) discloses a safety feedback control unit in which radiation resulting from overheating at the location of the surgery is detected and used to control fiber position, laser activation, or rate of pullback. U.S. Patent Publication No. 2009/0149845 (based on U.S. patent application Ser. No. 12/073,922) discloses a radiation feedback system in which a sensor at the treatment end of the fiber monitors wavelengths indicative of temperature at the treatment end so that overheating of tissues can be detected before the flash of light from pyrolytic burning occurs, and monitoring of the output of the laser by downstream deflection, absorption, or fiber movement in response to overheating detection. Many of the principles disclosed in U.S. Patent Publication Nos. 2009/0062782 and 2009/0149845 have been implemented in the LaserGuard™ system made by Optical Integrity, Inc. of Panama City, Fla.
One feature of the LaserGuard™ system is that it not only seeks to detect damage radiation from overheated tissues or instruments/devices, but also to enhance sampling detection by slightly bending a fiber anywhere along the fiber to leak non-coherent radiation caused by overheating and thereby detect the overheating while minimizing losses to the laser transmission are kept to a minimum. However, while the LaserGuard™ system has been effective in detecting overheating in a variety of laser surgery applications so as to prevent injury to the patient and protect other devices such as stone baskets and stone cones, it has been found that some treatment applications are still subject to overheating or burning of tissues, and that the likelihood of problems increases with the number of times a particular instrument is used. This is a critical problem given the cost of surgical instruments and the need to hold down costs if at all possible without sacrificing the safety of the patient.
The inventor has investigated the cause of continued overheating problems, even in systems with temperature or damage radiation feedback, and found that the cause can in many cases be traced to erosion or wear at the tips of the laser delivery instruments. This is particularly true where transmissive caps are provided at the end of the fiber, either to prevent fiber contact with tissues or to preserve the glass to air interface in a liquid environment. Unfortunately, the fiber cap surface erodes quickly when the fiber tip is buried into the tissue causing the temperature to rise. When that temperature exceeds 1000 degrees C., the cap absorbs infrared radiation due to free electron absorption, which can quickly erode the cap's surface and allow water into the cap destroying the glass to air interface. Continued lasing heats the water in the cap until the cap blows off like a bullet, sometimes lodging into surrounding tissue requiring surgical extraction.
It would seem that a feedback detection system should be able to detect the overheating before the cap is blown off. However, the feedback system has trouble detecting contact with a foreign surface because the surface prevents the damage radiation from reaching the detector, and therefore the amount of damage radiation available to the detector is relatively small. For example, if a partially transmitting surface is surrounded by a temperature conductive surface such as a tissue, much of the damage radiation will be absorbed by the conductive surface, and therefore will not reach the detector in time to enable termination or modulation of the laser energy being delivered and prevent damage caused by the overheating.
This invention addresses the problem of incomplete or delayed detection of overheating by providing sacrificial elements such as coatings or sheaths arranged to absorb damage radiation and emit warning radiation before the damage radiation would otherwise be detected by direct monitoring. In addition, coatings may be provided to enhance the detection of warning or damage radiation by, for example, increasing the contrast between the radiation to be detected and background radiation.
With respect to the embodiment in which the sacrificial element is a coating, those skilled in the art will appreciate that instrument coatings are known in the art. For example, U.S. Patent Publication No. 2009/0149845 mentions coating of the working channel of the catheter or introducer with Teflon™ or a similar protective material, so that an overheating fiber may be withdrawn into the working channel where damage will be minimal due to the protective effect of the coating. However, the known coatings are intended to be survive the treatment procedure, rather than being sacrificed before damage actually occurs.
With respect to the embodiment in which the sacrificial element takes the form of a sheath that surrounds the laser delivery fiber and serves to mechanically protect the instrument through which the fiber is inserted into the patient, the “sheath” of this embodiment differs from the conventional sheath in that it is designed to avoid affecting insertion of the fiber into the scope. Instead, its purpose is solely to absorb specific wavelengths of radiation in order to enhance detection of the radiation.
Those skilled in the art will of course appreciate that “sheaths” have long been used to protect surgical instruments inserted into a patient. For example, LISA Laser Products OHG of Katlenburg-Lindau, Germany sells disposable fiber insertion sheaths under the tradename FlexGuard™, which are used to guide fibers along a path established by bending the sheath, which remains deflected during insertion of the laser fiber. These sheaths are not suitable for use in connection with the present invention, and do not correspond to the sheaths described herein, not only because they are not designed to burn away upon overheating, thereby amplifying damage radiation, but also because the sheaths of the present invention are designed to be as flexible as possible so as not to interfere with positioning of the fiber.
In order to carry out the function of absorbing specific wavelengths of radiation while still maintaining flexibility, the sheath of the present invention must be relatively thin, whereas the FlexGuard™ sheaths must be thick enough to hold a particular shape when bent, and also to protect the inside of the working channel of a ureterorenoscope into which the fiber is inserted, as explained in LISA Laser Products product literature on the FlexGuard™ sheaths and in LISA Laser's U.S. Pat. No. 6,572,608. Unlike FlexGuard™, the sheath of the preferred embodiment is easily inserted at the same time as the fiber and therefore does not have the same limitations such as decreased water flow and loss of deflection because the scope is already in position and the fiber acts as a means to stiffen the polyimide or PET sheath.
The FlexGuard™ sheath is not the only prior sheath. Protective sheaths have been used in a variety of surgical applications, to protect optical fibers and other instruments such as the Nitinol shape memory instruments described in U.S. Pat. No. 6,966,906 (Brown) and U.S. Pat. No. 6,706,053 (Boylan), but none of the prior sheaths is designed to be sacrificed upon overheating in order to increase the detectability of damage radiation emitted during the overheating.